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Robust morphing materials take the strain

By Will Knight

Helicopter blades that change shape in mid-spin could be developed using a novel morphing material that works even under extreme stress and strain, researchers say.

A sturdy material that changes shape by “recharging” like a lithium ion battery, is being developed by a team of material scientists at MIT, the Swiss Federal Institute of Technology in Switzerland, and the University of Karlsruhe in Germany.

The morphing material is made from lithium cobalt oxide and graphite. Applying a current to the material causes ions to move between the two components. The process is the same as charging a battery – with negative ions being drawn towards the graphite and positively charged ions being drawn towards the lithium cobalt oxide.

This movement results in the ions becoming trapped between the lithium cobalt oxide and graphite molecules – so causing the material as a whole to expand. Reversing this chemical process reverses the shape change.

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Cars, boats, planes

In testing, researchers found the material expanded by as much as 19% and was also highly resistant to pressure, withstanding up to 200 megapascals. By contrast, piezoelectric materials – alternative shape changing materials which respond to an electric field – can only withstand one-tenth of this pressure.

The new morphing material also consumed just 5 volts, compared with the hundreds of volts required by piezoelectric materials.

This means the material could eventually be used to create morphing aircraft wings, boat hulls and car parts, the researchers suggest. “It’s capable of high stress,” says Yet-Ming Chiang, a member of the MIT team.

Jury out

The researchers have so far developed a simple airfoil that changes shape to achieve to different aerodynamic characteristics. Later this year they also hope to demonstrate prototype helicopter rotor blades that transform in mid-spin.

One expert on morphing aircraft design, who asked not to be named, agrees that existing materials have their limitations but says it is not yet clear what will be practical. “There is a long way to go and the jury is still out on the technology, particularly for applications such as morphing aircraft.”

Chiang admits that his material will have to undergo further testing before it can be used in real vehicles. “We’re still at the stage of trying to identify what the most successful materials will be and what the optimal design will be,” he says.